1. Field of the Invention
The present invention relates to a machining apparatus capable of changing the radial position of cutting edges of cutting tools, and more particularly to a technique for improving the rigidity or strength of a structure for supporting the cutting tools.
2. Discussion of the Prior Art
An example of a machining apparatus wherein the radial position of cutting tool bits or inserts can be changed is disclosed in laid-open Publication No. 62-92112 of unexamined Japanese Utility Model Application. This machining apparatus includes (a) a rotating shaft rotatable about an axis thereof, (b) an eccentric sleeve which is concentrically and rotatably supported by the rotating shaft, and which has an inner circumferential surface which is eccentric with the rotating shaft, (c) a tool holder which rotatably engages the inner circumferential surface of the eccentric sleeve and which is prevented from being rotated relative to the rotating shaft, (d) cutting tool bits carried by the tool holder such that the cutting edges of the tool bits are offset from the axis of the rotating shaft, and (e) a rotating device supported by the rotating shaft, for rotating the eccentric sleeve relative to the rotating shaft. In this machining apparatus, the tool holder engaging the eccentric sleeve is moved in the radial direction of the rotating shaft, when the eccentric sleeve is rotated by the rotating device relative to the rotating shaft. As a result, the position of the tool bits is changed in the radial direction of the rotating shaft.
However, the eccentric sleeve through which the tool holder is supported by the rotating shaft tends to reduce the strength or rigidity of the support structure for the tool bits, resulting in easy occurrence of strains or vibrations due to a cutting resistance during a machining operation. Thus, the conventional machining apparatus is limited in the machining accuracy and is not sufficiently capable of performing a heavy-duty machining operation.